Actual muscle strength potential varies as the muscle lengthens or shortens. With this in mind, muscle exercise may be characterized as follows:
(I) Passive exercise wherein the subject does not exert the muscular force producing the exercise motion. PA0 (II) Active exercise wherein the subject exerts the muscular force producing the exercise muscle movement.
(A) Categorized by direction of motion. PA1 (B) Categorized by response to muscle output.
(1) Concentric contraction wherein the muscle shortens while the subject is contracting against external resistance. PA2 (2) Eccentric contraction wherein the muscle lengthens while the subject is contracting against external resistance. PA2 (1) Isotonic contraction or exercise wherein the speed of the exercise motion varies in response to the magnitude of the muscular force. PA2 (2) Accommodating contraction or exercise wherein the resistance varies to equal to the exercising individual's voluntary force output.
(a) Constant resistance - concentric and eccentric contraction wherein the resistance is constant throughout the range of motion. PA3 (b) Variable resistance - concentric and eccentric contraction wherein the resistance is varied throughout the range of motion to a general strength curve for that movement. PA3 (a) Isometric contraction or exercise wherein the length of the muscle is held constant during a static contraction, so that the external assistance force varies in response to the magnitude of the muscle force. PA3 (b) Isokinetic contraction or exercise (concentric or eccentric) wherein the speed of the exercise motion is held constant during a dynamic movement, so that the external resistance force varies in response to the magnitude of the muscle force. PA4 (i) a one directional resistance with two and/or three dimensional movements PA4 (ii) a two directional resistance applied at a fixed radius about a fixed axis of rotation.
It is well known that the overall conditioning of an athlete is very important. For this reason, many athletes lift weights, run, stretch and generally play a variety of sports to remain in good condition. Additionally, numerous practice sessions are conducted wherein the specific movements important to the athlete during his particular athletic contest are practiced over and over again many times a week. For example, in baseball a hitter may take batting practice for a period of time each day. Similarly, a football kicker will simply kick a ball many times each day. Or, a hockey player will practice numerous slap shots day after day. Such practicing improves coordination and timing but another important aspect of the practice is the strengthening of the specific muscles which are used during the specific movement.
In a rehabilitation sense, U.S. Pat. No. 4,337,050 shows a recognition of the importance of isolating jointtype exercise movements for rehabilitating a specific muscle. The apparatus disclosed provides resistance about a fixed but adjustable rotating axis with an adjustable but fixed radius. This fixed radius does not allow for the elliptical type of two and/or three dimentional movements involved with training movements specific to athletic sports.
U.S. Pat. No. 3,567,219 shows an earlier version of similar apparatus. It provides for exercising by pushing or pulling an arm about a fixed axis.
With respect to sports, U.S. Pat. No. 2,134,451 shows the use of a baseball bat or a tennis racket attached to a weight hanging from a pulley system. Muscles are exercised to the extent that movement of the bat or racket in one direction requires a force equivalent to lifting the weight. U.S. Pat. No. 3,462,156 shows a similar idea for a golf club wherein the handle is connected with a cord to a retraction reel. U.S. Pat. No. 4,328,964 provides a more recent version of the same concept in that elastic ropes are fixed at one end and connected to various athletic instruments at the other end. Movement in one direction away from the fixed end of the ropes is resisted.
The devices of this latter group of patents provide a resisting stress for some of the muscles used during a particular athletic movement, but the design of the devices prevents the type of movement which would really be used during an athletic event and, furthermore, the devices provide resistance only in one direction while practicing any type of movement.
U.S. Pat. No. 3,738,661 discloses a golf exercising device which allows the exercising person to swing at an adjustable but fixed radius about an adjustable but fixed axis of rotation. Although many of the muscles used during a golf swing are exercised by this machine, the form of the swing is dictated.
U.S. Pat. No. 4,211,418 shows a different approach wherein an apparatus has a pair of rods at approximately 90 degrees with respect to each other. A rotational axis bisects the angle between the rods. The exercising person places a golf club in front of one rod and rotates the apparatus as the club is moved into a back swing. When the person stops, the apparatus rotates the rods 180 degrees so that the other rod makes contact with the front of the golf club. Then the person makes his foreswing while pushing the rod throughout the swing. Although the apparatus is less constraining than the device of the previously described patent, there is an artificial lag time at the top of the back swing and there would appear to be some safety problems with respect to the swinging rods, especially if the golf club were to slip off the rod or if the swinging rod made too fast an impact with the golf club as the person is at the top of his back swing.
It is clear that many exercising devices have been devised, some quite crude while others are more complex. None, however, allows for the elliptical type of two and/or three dimensional movements with accommodating resistance for training movements specific to athletic sports.